Effect of foliar spraying of Fe, Zn and Humic acid on some qualitative and quantitative traits of the apple (Malus damestica Borkh cv. Golden Delicious)

Introduction
Apple is from the Rosaceae family, which is the fourth most important fruit in the world and the most important fruit in temperate regions after citrus fruits, grapes and bananas (Janik et al., 2019). In high soil pH conditions, most micronutrient elements such as iron and zinc are deficient in apple trees. Foliar feeding is an effective way to compensate for the lack of micronutrients and increase their levels. The purpose of this research is to spray fertilizers containing iron, zinc and humic acid to achieve a suitable fertilizer combination to increase the yield and fruit quality of ‘Golden Delicious’ apple in response to the treatment of different concentrations of iron chelate, zinc sulfate and humic acid.
Materials and methods
In order to study the effect of three different concentrations of iron chelate, zinc sulfate and humic acid on some quantitative and qualitative traits of 13-year-old ‘Golden Delicious’ apple trees an experiment was carried out in the form of a completely randomized design with 9 treatment and three repetitions were performed. The treatments included foliar spraying with iron chelate, zinc sulfate and humic acid each at three levels (zero, 1000 and 2000 mg/L). Foliar spraying consisted of one stage before and four stages after flowering, the round of foliar spraying was done every two weeks.The first foliar spraying stage is on May 10 before flowering, the second foliar spraying stage is on May 25 after flowering and fruit formation, the third foliar spraying stage is on June 10 when the fruits are set, the fourth foliar spraying stage is on June 25 when the fruits were the size of walnuts, and finally, the fifth stage of foliar spraying was done on July 10, 2014, when the fruits were green and unripe. After the foliar application was completed, 21 healthy trees were selected for the experiment.The measured factors include length and diameter of the fruit, fruit density, dry weight of the fruit, total weight of the fruit, and measurement of the branch length of the current year, soluble solids, titratable acidity, pH, some nutritional elements in leaf and fruit. Data were analyzed using SAS statistical software version 1.9, and the comparison of averages was done using Duncan's multi-range test, and graphs were drawn using Excel version (2010) software.
Results and discussion
The effect of nutritional treatments on some quantitative and qualitative traits: The results indicated the significance effect of nutritional treatments observed on some quantitative traits such as fruit length (Table 1. Figure 1), the length of the branch of the current year (Table 1. Figure 3), fruit yield (Table 2, Figure 4), the density of fruits (Table 2. Figure 5). Also, the results indicated the significant effect of nutritional treatments on dry weight of fruits (Table 2, Figure 6), amount of iron element in leaf and fruit (Table 5, Figure 10; Table 6, Figure 13), the zinc element in the fruit is at the (Table 6. Figure 14). But these results, according to the results obtained, showed the opposite result, that is, it showed that the effect of nutritional treatments was not significant on some traits such as soluble total acidity (Table 4. Figure 8) and amount of potassium of fruit (Table 6. Figure 12).
Conclusions
The results obtained from this experiment, among the three fertilizer treatments used, the iron chelate fertilizer treatment with a concentration of 2000 mg/l had the greatest effect on some quantitative and qualitative characteristics of the leaves and fruits of the ‘Golden Delicious’ apple cultivar. This level of fertilizer treatment (2000 mg/L of iron) increased fruit yield, dry weight of fruit, iron element concentration in leaves and fruit. In general, the results of this research showed that in calcareous soils, iron and zinc foliar application can lead to the improvement of quantitative and qualitative characteristics of the ‘Golden Delicious’ apple cultivar.